SOMERVILLE — Campaign signs line the walls of a small basement room in a stout office building on Elm Street.

Many of these signs are written by hand on the backsides of discarded campaign posters for W. Mitt Romney and Shannon P. O’Brien.

A notice near the door reminds campaign staffers and volunteers to recycle. Half-empty bottles of Coca-Cola rest on the floor with a sleeping cocker spaniel.

A voice on the radio, tuned to election news, announces the day’s briefs.

“Starbucks against fair trade coffee? Couldn’t be!” Pat Keaney cries to the boombox from his desk near the door, where he is answering last-minute e-mail inquiries by undecided voters.

Keaney is campaign manager for Green Party gubernatorial candidate Jill E. Stein ’72-’73, and their campaign calls this unprepossessing room home.

As she returns to headquarters after a radio interview, Stein plans what she will do as voters head to the polls to determine the outcome of Massachusetts’ dead-heat governor’s race.

She polled around five percent in the final days before the election and became an increasingly important figure in the neck-and-neck struggle between Republican Romney and Democrat O’Brien.

Many Democrats said votes for the Green Party candidate could shift the election’s outcome in Romney’s favor.

Before heading out against from headquarters, Stein objects to her common portrayal as a “spoiler.” Her campaign, she says, has become a scapegoat for an unsuccessful Democratic effort.

“Republicans managed to win the last three gubernatorial races without the help of Greens,” she says. “The Democrats have to face the music.”

Stein works with Keaney to prepare an itinerary for the day. She and her supporters will visit some of the local polls to rally support.

Campaign staffer Michael Gainer, who spent the past few nights at headquarters, rolls up a rumpled sleeping bag.

Phones ring constantly. When a reporter from a local radio station calls Keaney, Stein rushes across the room with her notebook to speak with the reporter.

Her campaign is constantly hungry for media attention.